This application relates generally to vertical shaft-type furnaces and more particularly to apparatus for feeding solid particulates therein. This invention is particularly applicable for feeder arrangements for vertical shaft furnaces used in the direct reduction of iron ore wherein pelletized, lump, or sized iron ore mixed with fines constitutes the feed material. It will be appreciated by those skilled in the art that the invention has other applications and may be applied to any vertical furnace charged with particulate solids and heated gas for treating such solids which is passed in counter-flow relationship through a descending burden.
In vertical shaft furnaces for the direct reduction of iron ore, pellets, fines, lumps, etc. or a mixture thereof are charged to a shaft furnace through a hopper arrangement which feeds a number of charge tubes or feed legs, the lower ends of which terminate within the furnace near the external wall. The charge material forms a packed bed, or burden, in the furnace.
In accordance with the subject invention, a thermocouple is provided in the furnace wall to sense the temperature in the wall of the furnace near the stock line. The temperature rises or is high when the thermocouple is submerged in hot particulate material which entered the furnace through a feed leg tube, then became heated by the hot gases. Because of the excellent heat transfer in the packed bed between the hot gas and the burden, and the relatively high flow of reducing gas required in direct reduction relative to burden flow, the particulate material becomes heated to a temperature approaching the hot gas inlet temperature just a few inches (3 to 6 ) below the stock line. The pellets at the stock line have not yet become heated. When the temperature of the thermocouple increases, this indicates that no pellets are in its vicinity, that is, the stock line has dropped because its associated feed tube is plugged.
It is thus the principal object of this invention to provide a method and apparatus for detecting plugged feed legs in a shaft furnace.